1. Field of the Invention
The present invention relates to rotational angioplasty devices and, more particularly, to a rotational angioplasty device comprising a flexible drive shaft with an abrasive sleeve or crown mounted on the drive shaft.
2. Brief Description of Prior Developments
There are a number of different techniques and devices which have been developed for use in removal and/or repair of arteries and other similar body passages. One objective of some of the aforementioned devices and techniques is removal of atherosclerotic plaques from patient's arteries. Atherosclerosis is characterized by buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational angioplasty procedures are a common technique for removing such stenotic material. Such procedures are used most frequently to commence the opening of calcified lesions in coronary arteries. Often the rotational angioplasty procedure is not used alone, but is followed by a balloon angioplasty procedure. This, in turn, may frequently be followed by placement of a stent to assist in keeping the artery open. For noncalcified lesions, balloon angioplasty most often is used alone to open the artery, with stents often placed to keep the artery open. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience in-stent restenosis (i.e., blockage of the stent) which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. Rotational angioplasty devices were utilized in removing the excessive scar tissue from the stents and, thereby were useful in providing assistance in restoring the patency of the arteries.
It should be understood that rotational angioplasty devices and rotational angioplasty procedures are often referred to as rotational atherectomy devices and rotational atherectomy procedures. These terms may be used interchangeably herein.
One example of a rotational angioplasty device is shown in U.S. Pat. No. 4,990,134 (issued to Auth), wherein a front or distal portion of a burr is covered with an abrasive cutting material such as diamond particles. The diamond coated burr is mounted at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 140,000-180,000 rpm) while it is advanced across the stenosis. The burr has a solid cross-section and thus, as the burr is removing stenotic tissue, it also blocks blood flow through the artery. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. A series of different size burrs may be utilized to open the artery to a desired diameter. U.S. Pat. No. 5,987,566 (issued to Shturman) shows another rotational angioplasty device having a drive shaft made from helically wound wires. A section of the drive shaft has an enlarged diameter. In one embodiment at least a front or distal segment of this enlarged diameter section is covered with an abrasive material to define an abrasive segment of the drive shaft. The enlarged diameter section is hollow. This Shturman Device of the '566 patent is capable of opening an artery only to a diameter about equal to the maximum diameter of the enlarged diameter section of the drive shaft, thereby providing results similar to the Auth Device of the '139 patent. The Shturman Device of the '566 patent possesses certain advantages over the Auth Device of the '139 patent because it is more flexible.
Another example of a rotational angioplasty device is provided in U.S. Pat. No. 6,132,444 (issued to Shturman et al.) which describes a rotational atherectomy device having a flexible, elongated, rotatable drive shaft with an asymmetric or eccentric enlarged diameter section. At least part of the eccentric enlarged diameter section has an abrasive surface which defines a tissue removing segment of the drive shaft. When placed within an artery against stenotic tissue and rotated at sufficiently high speeds (e.g. in the range of about 40,000 rpm to about 200,000 rpm) the eccentric nature of the enlarged diameter section of the drive shaft causes its abrasive segment to rotate in such a fashion as to open the stenotic lesion to a diameter substantially larger than the maximum diameter of the enlarged diameter section. Preferably the eccentric enlarged diameter section of the drive shaft has a center of mass spaced radially from the rotational axis of the drive shaft, facilitating the ability of the device to open the stenotic lesion to a diameter substantially larger than the maximum diameter of the enlarged diameter section. Typically this is achieved by constructing the enlarged diameter section of the drive shaft asymmetrically (i.e., spacing the geometric center of the eccentric enlarged diameter section of the drive shaft away from the rotational axis of the drive shaft). A drive shaft having an eccentric enlarged diameter tissue removal section with a diameter of not more than 2 mm is capable of opening stenotic lesions to a diameter equal to the original diameter of the coronary arteries (i.e., to a diameter of more than 3 mm) so that in a significant percentage of cases balloon angioplasty may not be needed to complete the procedure. The device is particularly useful for cleaning out partially blocked stents. The external coating or cover of abrasive material in Shturman Device described in '444 patent is applied directly to the wire turns of the helically wound wires, which make up the drive shaft. Application of abrasive material directly to the wire turns of the drive shaft is difficult and expensive due to a need to mask portions of the drive shaft which should not be coated with abrasive material. Direct deposition of abrasive material on the outer surface of the wire turns of the drive shaft is further complicated by any spaces between adjacent wire turns which are larger than what is acceptable for conventional abrasive material (diamonds) deposition techniques (e.g. electroplating). It should be also mentioned that electroplating of diamonds directly to the surface of the wire turns of the drive shaft requires chemical treatment of the surface of the wire turns prior to electroplating of the diamonds. Removing chemicals prior to or after electroplating of the diamonds is also difficult. The above described problems, which are associated with the direct deposition of abrasive material (diamonds) on the wire turns of the drive shaft made manufacture of the abrasive drive shafts unreliable and expensive. The present invention overcomes the problems associated with the direct deposition of the abrasive material on the wire turns of the drive shaft.